how to prep a d&d session

How to Prep a D&D Session

Welcome to the post of The Arcanery Lab Notes!

I went back and forth on what to write about here. Since it’s the first post should I start with a post about session zeroes? Should I go earlier and do a post on campaign creation? So many options! And then I realized that what I was trying to do for this post is something that I do for each session I GM. And so, we’re going to talk about Session Prep!

Prep is possibly the hardest part of being a GM, and is definitely the most time consuming, but it is also the part that ensures you and your players are going to have fun. There are certainly games out there that are “zero prep” (although I still do some prep for them), and there are games that don’t even require a GM. But for your classic TTRPGs, whether it be the world’s oldest or something on the cutting edge, prep is a life saver. 

There are plenty of different ways to prep, you can scour the bestiaries for combat inspiration, you can write out some backstory for an interesting NPC that you want to introduce, create an interesting scene for the party to run through, or even just draw out a map. But whatever tactic you take, having something prepped will make your session run smoother, you’ll feel less stress, and it will maximize your fun.

So let’s prep a session! 

The Setup

Before we do anything we need to establish where we are in the campaign, and what type of encounters you want in this session.

The players in one of my D&D campaigns have recently found out that a corrupted tree that they’ve been questing to find a cure for has bloomed and taken over the nearby town which has been their home base for a while (and the childhood home of one of the characters.) So they’re rushing back to try and save whoever they can, and cut down this tree of eeeeeeevil. So, what are our knowns?

Known Circumstances ~or~ Where are the heroes now?

We have 4 important known circumstances for this session:

  1. They have to get to the tree.
  2. They have to destroy the tree. 
  3. The townspeople have become thralls to the tree due to the spores that it has been releasing into the air, and will defend it (dramatic!)
  4. Unbeknownst to the party the tree has been activated not by the spore druid that they defeated earlier in the campaign, but by an ancient seraphim.

Looking at our known circumstances I can tell that I want 3 different encounters. I need to have some sort of travel encounter as they get there, I want there to be some dialogue between the seraphim, the townsfolk, and the party, and I want there to be a BIG FIGHT.

Let’s break that down.

How do you get them to the encounter?

In order to run the encounter, you have to make sure the party gets to the encounter! For my session, they have some traveling to do as they are a day and a half away from the location. I also need to keep in mind how long my session is going to be. I want them to have enough time for the combat since I’m planning on it being a big battle. So I think I’ll montage past traveling a little, but there are two scenes that I want to play out on the road. 

Encounters as Atmosphere

I want the players to see the effects that the tree is having on the world and build some atmosphere to the session. The goal is to start ramping up the tension well before the battle, get the players on the edge of their seats, and get them to start realizing what they’re facing. So how do we do that? For this session we’ll do a little scouting side scene to see the bubble that has surrounded the area, and then an overnight scene where they are overtaken by a spore cloud. The bubble to show the level of reality warping, and the spore cloud will force them to make Constitution Saves or be poisoned and gain a point of exhaustion.

Pre Combat Interaction

Diving straight into a fight can be a lot of fun, and surprise rounds are great whether the heroes or the villains get one. But sometimes you want there to be an interaction first. Something to really make the party want to fight, and something to help set the tone and stakes. Since my battle here is supposed to be momentous, I’m going to build that in.

In order to do that for this session, I want to build a couple of scenes. I want an interaction with the angel (whom they have met once before), an interaction between one of the PCs and their mother who has become a thrall.

Villainous Motivation

dnd monster

It’s important for characters to have motivation. I personally like creating complex characters, but a villain’s motivation can be really simple. Whatever your style is, find a reason for your villain to be fighting. This topic deserves it’s own post, so I won’t go in depth on what I do for choosing motivation but here’s a quick overview of how I prepped the NPCs for this encounter:

The angel is an antagonist who appeared earlier in the campaign, and whose motivation is sweeping. They are here to complete a phase of their long term plan which I laid out when I was building the campaign (we’ll do an article on campaign building to

o!) so I don’t feel I need to prep much for them. I’ve played this NPC before, so I know I can improvise my dialogue based on character responses, but I’m going to take a couple of quick notes on them to remind myself: They want to spread their “love”, they appear very serene but are swift to lose their temper, they don’t have a stat block but they have 3 legendary resistances and are going to vanish on their first turn after initiative. I’ll probably put these on a post-it and stick it somewhere that will catch my eye.

The mom interaction is going to be more in depth and require digging through my notes and the character’s backstory, so I’ll save that one for later (and perhaps its own post) and move on to planning the COMBAT!


Prepping for Combat Part I – Monsters!

Can’t have combat without something to fight, so we need to figure out what kind of enemies are there? Well, for this fight we have all the townsfolk who have been thralled, and there’s the tree. Not quite enough for this fight. This fight is the culmination of an entire arc so I want it to feel epic. I want it to feel like it could be an end of the campaign battle (even though the campaign will continue) and I want there to be a real threat of a TPK. BUT, I also need to remember that the party will not have a long rest (long rests are a week in this campaign) before this fight, and 2 of them already have a point of exhaustion. On top of that it’s possible that the party could gain a point of exhaustion or the poisoned condition from the sporecloud that night. 

Choose Your Fighter

So keeping ALL that in mind, what monsters should I use? Well, the last time they were here they fought blights and myconids, so let’s do some thornys. They can help corral the party and cut off their escape route. They can also harass them without doing too much damage, and help balance the action economy. For the tree itself I really like a lot of the actions a corpse flower has, and I like how that fits in with the thralling. So I’m going to start with that as a base and then tweak it to be more tree and more mushroomy. I also want this to feel urgent, so I’ll give it either a lair or legendary action to cause an enthralled villager to kill themself in order to restock the corpses that the tree has absorbed. And let’s give the tree a damage threshold. For our tree we’ll say it has a damage threshold of 10 until it is at half health, and then it becomes a threshold of 5 (to show that the party is chipping away at its outer bark.) We’ll probably give it a few more lair and legendary actions. I’ll look up some more powerful myconids and some undead to see what feels right.

dnd fighter

Using Backstory to Create Stats

Now for the townsfolk! What could hurt more than having to fight against your friends and loved ones? 

The head of the local crafting guild is there (she’s also a patron of the party). She comes from a long line of archers, so we’ll start with a scout stat block for her – but we’re going to increase her AC and HP and boost her hit bonus with the bow. And then, because I’m nasty, let’s give her a reaction. She’s primarily a ranged fighter, so let’s say that once per day she can release a spore cloud if someone comes within 5’ of her. Maybe a paralyzing spore so that she can move away without being in danger of an opportunity attack.

The head of the watch is also there, and I want her to feel visceral and kinda wicked. So I’ve looked through the bestiaries and the campaign settings, and I’ve been thinking about the blood hunter block from Wildmount. A couple of tweaks to make that more plant/spore-y and that’s exactly the level of intensity for her. Blood curses and fungal poison. Not to mention the visuals of her cutting into herself.

Most of the townsfolk are just going to be thralls for the tree to either eat and regain hp or turn into zombies, so the last of our specifics is going to be Ma. As far as the characters know, Ma is just a normal human woman. But now she’s a thrall, so why don’t we reflavor a green hag to feel more shroomy? And we’ll give her a mass healing spore to hopefully keep some of the townsfolk alive through the end of the battle. Shame if they defeat the tree but don’t manage to save anyone.


Bring on the Minions

The corpse flower has a mechanic to spit out zombies, so the LAST thing we’re going to do is double check that we’re happy with those stats. Even though these are really just minions to balance the action economy in the baddie’s favor, I think zombies are a little weak for this fight. And more importantly, plain zombies aren’t as interesting to me as the rest of the monsters. So I’m going to tweak and flavor them. Now they’re spore zombies. I’ll give them a small chance to explode every time they take a hit (probably 5%), and give them an action to sacrifice themselves in a burst of poisonous shroom spores. The tree will start with some zombie inside it, which I will roll to randomize at the start of the session, and it can restock by causing the townsfolk to sacrifice themselves. 

And that’s a combat setup! Time to Roll Initiative!


If they manage to defeat the tree, the village is saved! At least everyone who survived the fight is. 

Rewarding your players

Now some rewards! This campaign is VERY low magic. They’re level 4 and they have not even seen a magic item yet. So we have to come up with something else. We’re using milestone leveling, and this is a level up for sure, so that’s a reward. 

I’m also a big fan of boons. I think they’re a fun way to show character growth and to give out some abilities or powers that will make adventuring more exciting. So I’m going to craft some personal rewards for them themed after this fight. I’m going to give the cleric a 3x per long rest “healing spore” (reskinned healing word), and the barbarian will get a special “spore aura” that gives some temp hp and limited telepathy. The druid is getting a bump to the wildshape ability increasing the amount of time it lasts. I still need to come up with something for our rogue and our ranger, so if you have a good idea for a reward toss it in the comments!

Finally they’re going to be, once again, the heroes of the town which will come with additional perks when they’re in the area.

And that’s it! A full session prepped. It’s a combat heavy one, so we’ll talk more in depth another time about how I prep for social and exploration scenes, along with what and how much I prep for the chances that the party will make a hard left and end up somewhere I was completely not expecting (for instance if a wild magic surge causes a portal to open and then they decide to enter it.) 



Quick recap of our major points:

  • Where are your players now? What’s their location and what’s their health/condition status?
  • What are your given circumstances?
  • What’s the purpose of your encounters? Atmosphere, plot, combat, diversion?
  • What motivation does your antagonist have?
  • What monsters do you want to use and do you want to tweak them?
  • What resolution are you looking for?
  • How do you reward your players?

For a deeper dive on this you can listen to our podcast episode “Let’s Talk About Prep!” and let us know in the comments what you do differently when you prep for your big battles!

Posted in DM Help, DM Tips, Session Prep.